Patent GB-427732-A (GB)
Title: Improvements in photographic processes and materials therefor
IPC: G03C1/54
Filed: 1933-10-16
Abstract: Photographic prints are produced by the use of a carrier provided with a benzene diazo-compound which upon exposure in the presence of water forms primarily a phenol so substituted in the benzene nucleus that it can be oxidized by the benzene diazo-compound itself or another benzene diazo-compound present in the layer to form a coloured product, the material of the carrier being such that the speed at which the oxidation proceeds is greater than that at which the diazo-compound couples with the phenol to form an azo dye, the diazo-compound being substituted in the nucleus by one or more alkyl or aryl groups.  Examples are given of the use of (1) the diazo compound produced by treating 4 : 4<1> - diamino - 3 - oxydiphenyl - 6 - sulphonic acid with sodium nitrite in hydrochloric acid solution, the compound being applied to paper together with copper nitrate; (2) 6 - methyl - 1 - hydroxy - 2 - diazonium-benzene-4-sulphonic acid, applied to paper along with copper nitrate; (3) 1 - hydroxy - 2 - diazo - 5 - methyl - 4 - benzene sulphonic acid used as in (2) above or with the addition of sodium-2-naphthalene sulphonate or sodium bicarbonate; (4) 3 : 3<1> - dioxy - 4 : 4<1> - tetrazodiphenyl - 6 : 6<1> - disulphonic acid applied to paper along with copper nitrate and dried by means of phosphorus pentoxide; (5) 5 : 5<1> - tetrazo - 4 : 4<1> - dioxy - diphenyl - 2 : 2<1\h - di<>sulphonic acid used as> under (4) above; (6) 2 : 2<1> - dimethyl - 3 : 3<1> - dioxy - 4 : 4<1> - tetrazodiphenyl - 6 : 6<1> - disulphonic acid used on paper with or without copper nitrate; (7) 1 - hydroxy - 2 - methyl - 6 - diazonium benzene - 4 - sulphonic acid applied with copper nitrate to paper coated with casein, gelatin, or agar-agar; and (8) 2 - diazo - 1 - oxy - 5 - methyl-benzene-4-sulphonic acid applied with copper nitrate to gelatin coated paper.  This layer may be after-treated with ammoniacal copper solution.  3 : 3<1> - dioxy - 4 : 4<1> - tetrazodiphenyl - 6 : 6<1> - disulphonic acid is prepared by first reducing a solution of 1 - oxy - 2 - nitrobenzene - 4 - sulphonic acid in KOH with zinc powder, treating the product with HC1 which converts it into 3 : 3<1> - dioxy - 4 : 4<1> - diamino - diphenyl - 6 : 6<1> - disulphonic acid and diazotizing the latter in solution in HC1 with sodium nitrite.  5 : 5<1> - tetrazo - 4 : 4<1> - dioxydiphenyl - 2 : 2<1> - disulphonic acid is formed by converting the potassium salt of 3-nitrobenzene-1-sulphonic acid into 4 : 4<1> - diaminodiphenyl - 2 : 2<1> - disulphonic acid, diazotizing this and decomposing the diazo compound with steam in the presence of sulphuric acid, nitrating the product, reducing it with stannous chloride and diazotizing the resulting 5 : 5<1> - diamino - 4 : 4<1> - dioxydiphenyl - 2 : 2<1> - disulphonic acid.  2 : 2<1> - dimethyl - 3 : 3<1> - dioxy - 4 : 4<1> - tetrazo - diphenyl - 6 : 6<1> - disulphonic acid is prepared by first reducing 1 - hydroxy - 2 - methyl - 6 - nitrobenzene-4-sulphonic acid in solution in KOH with zinc powder and diazotizing the product with HC1 and sodium nitrite.